oo THE BIOLOGY OF THE AlflMAL 



tween " body-cavity," in which various internal organs 

 might be contained, and the "digestive cavity" in a 

 zooid ? If not, would you consider these two cavities 

 to be one and the same as regards these hydroids? 

 Compare with Hydra. What means of oflfence and of 

 defence have these hydroids ? Of distribution ? Which 

 do you regard as the higher animal, a oampanularian 

 hydroid or a hydra ? Why ? How much of the colony 

 do you regard as an individual animal ? Why % 



Compare with this organism any other hydroids that 

 may be available, also the sea-anemone {Metridium). 



